The invention relates to a composite substrate with high thermal conduction, applicable more especially to the manufacture of cases for electric components or circuits formed on a wafer of semiconductor material.
Electric components or circuits of this type are usually contained in a case, comprising a base or substrate, and a cover applied hermetically to the base, this latter or the cover-base junction having the output connections of the circuit passing therethrough.
As is known, the dissipation of heat in these encased circuits creates difficulties, particularly in the case of large-scale integrated circuits and power components, where the dissipation is particularly high. The main requirements with which such a case must comply are the following: the thermal expansion coefficient of the substrate must be as close as possible to that of the semiconductor used; the component elements of the case, and more particularly the substrate thereof, must have as high a thermal conduction as possible for evacuating the heat; the substrate must be electrically insulating, at least partially, so as to avoid any short-circuit between the output connections of the circuit; in some applications, it is even necessary for the substrate to be completely insulating.
It is known in this connection to form a substrate from beryllium oxide; in fact, this material is electrically insulating, it has an expansion coefficient close to that of silicon and it has good thermal conduction. However, it is a very toxic material, the industrial production and handling of which poses numerous safety problems and it is in addition rare and expensive.